Photoluminescence, modulation spectroscopy and surface photovoltage characterization of quaternary Zn1-x-yCdxMgySe compounds

Abstract

An optical characterization of wurtzite Zn1-x-yCdxMgySe crystalline alloys grown by the modified high-pressure Bridgman method has been carried out by temperature-dependent photoluminescence (PL) and contactless electroreflectance (CER) in the temperature range of 10300 K, and photoreflectance (PR) measurements between 300400 K as well as surface photovoltage spectroscopy (SPS) at 300 K. Low temperature PL spectra of the investigated samples consist of an excitonic line, the “edge emission” due to radiative recombination of shallow donor-acceptor pairs and a broad band related to recombination through deep level defects. Three excitonic features, A, B and C, in the vicinity of band edge were observed in the CER and PR spectra. The peak positions of band-edge excitonic features in the PL spectra are shifted slightly towards lower energies as compared to the lowest corresponding transition energies of A exciton determined from CER and PR data. The increase of the CER-PL shift with the increasing of Mg content in the investigated crystals is explained by the rising of compositional disorder causing the smearing of the band-edge energies. In addition, the coincidence of energy positions of features obtained from SPS measurements with excitonic transition energies E0A determined from CER/PR data at 300 K confirm the proper surface treatment of the samples.